It's a 'ring' where I gluewaterproof polish paper P4000 on.
这是一个'环'我胶水防水波兰文件p 4000上。
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The modification has been made on the black wattle tannin adhesive with sodium sulfite and the MUF concentrate so as to prepare out a tannin adhesive with good water-proof and better glue properties.
Rib of slab has prominent water-proof capability. It is fixed by hidden key without any glue. No bolt on the outside surface which prevent from pollution and aging.